1. Field of the invention
The present invention relates to a switching circuit to limit surge into lamp, specifically, a single-wired switching circuit directed to limit surge into lamp.
2. Description of the prior art
One of the major causes of lamp outage is the switchon surge that may be 10-fold larger or more than the current in the stationary state. For example, the current across 100 watt lamp exhibiting a filament resistance of 100 ohms in the stationary state is one ampere when energized with 100 volts. Since the filament resistance at ambient temperature is about 10 ohms, a surge of 14 amperes (=140 volts/10 ohms) arises and its magnitude is 14-fold larger than that in the stationary state when the filament is energized with conventional ac 100 volts at its peak, i.e. 140 volts.
U.S. Pats. Nos. 4,555,741 and 4,572,992 disclose that the voltage drop across diodes is used to actuate switching devices, such as magnetic relay and thyristor, to regulate the current across loads including lamp and electric motor.